Carbohydrates and glycol-conjugates are substrates for glycosyl transferases (GTs) and glycoside hydrolases (GHs). The structure of glycoside hydrolases began to be solved starting from the 1980s. At the same time, new GH proteins were discovered and their amino acid sequence determined. Two main observations emerged from the new data. 1) The classical E.C. nomenclature system for naming enzyme families was not precise enough to classify the increasing number of enzymes that had different structure yet performed the same enzymatic reaction. 2) Enzymes related by homology could have different enzymatic activity thus also making the E.C. nomenclature system confusing for these related enzymes.
A new family based nomenclature system was proposed by Bernard Henrissat in 1991 based on the structure of the enzymes (Henrissat B., A classification of glycosyl hydrolases based on amino-acid sequence similarities. Biochem. J. 280:309-316 (1991); Henrissat B., Bairoch A. New families in the classification of glycosyl hydrolases based on amino-acid sequence similarities. Biochem. J. 293:781-788 (1993); Henrissat B., Bairoch A. Updating the sequence-based classification of glycosyl hydrolases. Biochem. J. 316:695-696 (1996) and Davies G., Henrissat B. Structures and mechanisms of glycosyl hydrolases. Structure 3:853-859 (1995).). Updated classifications are available on the Carbohydrate-Active EnZymes website (CAZy).
The classification of glycoside hydrolases in families based on amino acid sequence similarities was introduced because there is a direct relationship between sequence and folding similarities, and such a classification is expected to:                (i) reflect the structural features of the enzymes, which cannot be reflected by the substrate specificity alone,        (ii) help to reveal the evolutionary relationships between the enzymes, and        (iii) provide a convenient tool to derive mechanistic information.        
Amino acid sequences grouped by nature of their similarity to a particular GH family can give ideas as to the activity of the new hypothetical protein. Some of these amino acid sequences, grouped in a GH family by homology have later been suggested to have certain enzymatic activity. So, in short, grouping a new amino acid sequence in a GH family does not specifically indicate the exact enzymatic activity. The enzymatic activity must be demonstrated by an activity assay of the cloned or purified protein. If the assay is difficult determination of the proteins actual function can remain un-revealed for years.
Glycoside hydrolase family 8 (GH8) comprises enzymes with several known activities; endoglucanase (EC:3.2.1.4); lichenase (EC:3.2.1.73); chitosanase (EC:3.2.1.132).
Some xylanases are inhibited by components found in flour which makes them unsuitable for the manufacture of products based on a dough. GH8 xylanases are not inhibited by components in dough and they require only a very low dosage in the dough to provide a volume increase in the baked bread. Unfortunately, as is well-known in the art of baking, use of any of the naturally occurring GH8 xylanases identified to date results in a sticky dough which is problematic to handle.